There is a type of precast concrete pile used in the underpinning of building foundations comprised of vertically stacked, unconnected, precast concrete segments. These segments are pressed or driven vertically into the soil one at a time until adequate load capacity is obtained. This type of pile is distinctive in that it can be installed with almost no clearance, usually beneath an existing structure.
Although serviceable, this pile has several significant disadvantages: (a) the pile segments are not aligned, other than being stacked on each other, and detrimental misalignments can occur, (b) independent inspection of the installed pile depth is only possible by providing full-time inspection personnel during installation to monitor the quantity of pile segments used at each pile location, and (c) the complete pile is an unreinforced stack of precast concrete segments.
Misalignment of the segments as they are installed can produce several conditions detrimental to the future pile stability. Lack of proper independent inspection of pile depth can lead to inadequate pile penetration, which in highly expansive soils produces an unstable installation subject to continued movements caused by seasonal change in soil moisture. An unreinforced or non-continuously reinforced pile is subject to permanent separation at segment joints or breakage at segment midpoints when installed in clay soils having high shrink-swell potentials.
Under certain circumstances, the under-consolidated soil conditions into which pile segments are installed can have a "chicken pot pie" configuration. In other words, the surface of the earth is a stiff crust which is supported upon a softer layer which is, in turn, supported upon a denser layer. In the past, it has been the practice in certain areas of the country, such as the Louisiana area, to insert timber piles into such types of earth. These timber piles can have a length of thirty feet or more which would be intended to extend through the softer layer so as to be supported upon the lower denser layer of such soil configurations. Unfortunately, such timber piles sometimes have inadequate lengths for extending entirely through the softer layer. If the bottom end of the timber piles fail to contact the lower denser layer of the earth, the timber pile can subsequently sink through the softer layer. As a result, the building foundation can excessively settle with the supported structure thereon.
In the past, various patents have issued relating to the devices for installing underpinning piles retroactively for the support of a structure. For example, U.S. Pat. No. 5,288,175, issued on Feb. 22, 1994, to D. W. Knight, describes a continuously reinforced segmental precast concrete underpinning pile which uses a method of installing where a high strength strand aligns the precast segments during installation. The strand provides a means for measurement of the pile penetration depth. The strand continuously reinforces the pile when bonded or anchored upon completion. This patent describes a further process whereby a strand is affixed to a first pile segment prior to being driven into the earth. The first pile segment, along with the attached strand, is driven a desired distance into the earth from the supporting structure. The strand will extend outwardly from an end of the first pile segment. The second pile segment then slides along the strand until the second pile segment contacts an end of the first pile segment. The second pile segment is then driven into the earth for a desired distance. Ultimately, after each of the pile segments is driven a desired distance into the earth, a cap member is affixed to the top of the array of pile segments so as to be placed in proximity under the foundation of the structure. In the "chicken pot pie" type soil conditions, the method of this patent fails to utilize existing pile structures. As such, there is a considerable cost associated with the driving of multiple piles segments through the softer layer of the earth. Under such soil structures, it would be desirable to use the existing pile structures if possible.
U.S. Pat. No. 5,399,055, issued on Mar. 25, 1995, to E. T. Dutton, Jr., teaches a device and method to level and repair a failed concrete foundation. A series of cylindrical pile segments are jacked into the soil with water jetting to a pre-determined depth. This is used so as to attain sufficient skin friction. Reinforcing steel is inserted into the stacked column of cylindrical pile segments and grout is further pumped into the cylindrical pile segments to suitably fix the reinforcing steel to the inside ofthe cylindrical piles. This forms a single shaft pile so as to eliminate or reduce pile deflection and sheer. Once again, the patent fails to make use of existing timber piles.
It is an object of the present invention to provide a method of installing pile segments for supporting a structure upon the earth.
It is another object of the present invention to provide a method of installing pile segments which makes use of existing timber piles below the structure.
It is another object of the present invention to provide a method of installing pile segments which minimizes the number of pile segments required for the support of the building.
It is a further object of the present invention to provide a method of installing pile segments which more suitably supports a structure on a "chicken pot pie" type earth structure.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.